1. Field of the Invention
The present invention relates generally to control circuits for incremental positioning encoders and more particularly to a digital logic circuit particularly adapted for use with an incremental position type encoder.
2. Description of the Prior Art
Encoders are important components of motion control systems. For closed-loop control, encoders are used to feedback the actual position and/or speed of a device for comparison with a reference corresponding to a desired position and/or speed. Open-loop systems often have encoders coupled to their movable members, such a motor output shafts, for providing signals indicating direction of motion and the distance to the final desired position. Typically, encoders generate two quadrature pulse train signals to increase resolution and to decide the moving direction of, for example, an associated output shaft. More specifically, this happens in disk drives which utilize tracking error signals to generate quadrature signals to indicate the position of a read/write head with respect to a disk track. To convert the quadrature signals, generally two pulse trains, to position information, an electronic circuit incorporating digital logic components is used. The circuit accepts the two quadrature pulse trains and converts them to a counting CLOCK signal and an UP/DOWN count signal. By passing the signals through a counter circuit, which counts a net number of the count pulses, a position information signal can be obtained.
A patent of interest for its teaching in this art is U.S. Pat. No. 3,843,915 entitled "Servo-Motor Control System Including A Two Phase Digital Shaft Position Detector" by J. E. Helmbold.
Another patent of interest for its teachings in U.S. Pat. No. 4,481,569 entitled "Feedback System For Robot Controller" by S. A. Hoodbhoy.
The digital logic circuits used in the above referenced patents use an external clock and a flip/flop circuit to detect the edge of each pulse in a pair of pulse trains. After obtaining the edge signals for each of the two pulse trains, an UP/DOWN count signal and count pulse signals are generated. The UP/DOWN count signal and the counting pulse signals are then used as the input signals to a counter. The output signal from the counter is the position information signal which then can be used to activate, for example, a closed-loop servo controller.